The usual light or UV binocular microscope contains a single objective lens which functions to produce a magnified image of the subject to be viewed, and dual ocular lenses for viewing the magnified image through right and left eyes. Since the image that is viewed through the oculars is formed by a single objective, the viewer has no perception of depth. As a consequence, it is often difficult to visualize how the magnified object appears in three dimensions, and this greatly limits the information available to the viewer, particularly when viewing specimens, such as external biological structures, in which the spatial arrangement of parts is unclear without depth references. Usually it is necessary to view such specimens through a series of focal planes in order to obtain depth information, a generally unsatisfactory approach, since the entire object cannot be viewed at one time. Also, the effort required to compensate for lack of three dimensional structure contributes to fatigue in normal microscope use.
Three-dimensional microscopes have been developed for and are widely used in microsurgery. These scopes are constructed somewhat like conventional binocular telescopes, in that they contain a pair of lens systems, each of which includes an objective lens and an ocular for viewing the magnified image produced by the associated objective. Thus the right and left sides of the subject under examination are viewed separately by right and left eyes, respectively, giving a three-dimensional image. One limitation of stereobinocular microscopes of this type is that the individual lens systems cannot be accurately focused on a single object region at a magnification much beyond about 40 power--a range that is normally adequate for microsurgical work, but not for general microscope applications. The surgical stereomicroscope is also relatively costly, since two separate lens systems are required and the device must be made with a high degree of precision.
Proposals have been made in the prior art for stereoscopic viewing at high magnification, but these have been rather complex mechanical systems that are not readily adaptable to a precision optical instrument. For example, microscopic systems having oscillating shutters which rapidly and recurrently switch between right and left oculars, giving a partial illusion of depth, have been proposed.
Stereoscopic binocular telescopes are, of course, well known and widely used. In general construction, binocular telescopes include separate left and right optical systems, each containing objective and ocular elements, for viewing a distant object simultaneously by left and right eyes. Binocular telescopes are quite satisfactory for intermediate telescope power, and are only limited in power by the size and cost of the individual optical systems. In this regard, it is noted that the monocular optical systems are doubled, and their mechanical perfection is critical to acceptable stereoscopic viewing.